TRAPPIST-1 and its compact system of temperate rocky planets

TL;DR

The TRAPPIST-1 system, with seven Earth-sized planets including three in the habitable zone, offers a unique opportunity for detailed characterization of rocky exoplanets and their atmospheres using transit and thermal emission observations.

Contribution

This study provides precise measurements of the masses, densities, and atmospheric properties of the TRAPPIST-1 planets, highlighting their potential for future atmospheric characterization.

Findings

No extended primary atmospheres detected around the seven planets.

Inner planets likely have low-density atmospheres or are bare rocks.

Outer planets may host dense secondary atmospheres detectable with JWST.

Abstract

The TRAPPIST-1 system is comprised of seven Earth-sized rocky planets in small orbits around a Jupiter-sized ultracool dwarf star 12 parsec away. These planets cover an irradiation range similar to the range of the inner solar system. Three of them orbit within the circumstellar habitable zone. All of them are particularly well-suited for detailed characterization, thanks to the small size of and to the infrared brightness of the host star, and to the system's compact resonant structure. An intense transit-timing monitoring campaign resulted in unprecedented precisions on the planets' masses and densities, and in strong constraints on their compositions. Transit transmission spectroscopy with HST discarded the presence of extended primary atmospheres around the seven planets. The first thermal emission measurements obtained with JWST favor low-density-atmosphere or bare-rock scenarios for the two inner planets. The detection of dense secondary atmospheres around the five outer planets could be achieved by transit transmission spectroscopy with JWST, but this will require addressing the critical problem of stellar contamination with more theoretical and observational work.